This invention relates to a cylindrical elastomeric bearing with wide angular deflection and being relatively rigid radially, which is mounted between an inner sleeve and an outer sleeve, in such a way that the outer sleeve and the inner sleeve can rotate in relation to each other about their common axis with virtually no possibility of radial deflection. These types of cylindrical elastomeric bearings, in accordance with the invention, which function without any lubrication, can be mounted in particular on a gyroplane rotor head between the hub body and each blade to form a pitch changing articulation for the blades.
Many types of bearings are already known that offer some flexibility between the inner part and outer part, and which are used in particular in the structures that connect each of the blades of a gyroplane to the body of the rotor hub.
French Patent No. 2 358 316 refers to these types of connecting structures, its object being a helicopter rotor comprising a rotor hub that rotates about a substantially vertical axis, and which includes a set of rotor blades. According to this patent, the hub is provided, for each blade, with a bending element which extends substantially radially from the hub, and which is elastically flexible in the blade's beating plane. In accordance with this invention, the hub comprises a pitch changing articulation at the end turned towards the outside of the bending element, and which comprises a substantially tubular portion. This substantially tubular portion is fitted, on the side of the end turned towards the outside, with means for fixing the rotor blade. Moreover, this tubular portion is fitted so as to pivot on an inner bearing and an outer bearing, in relation to the axis of the rotor. These two bearings are made of an elastomer, and are mounted separately from each other on a spindle which extends the bending element. An elastic assembly designed to work in shear is associated with the outer bearing so as to allow drag movements of the tubular portion and of its associated blade. These drag movements are made about the geometric center of the inner bearing. The inner bearing comprises two elementary elastomeric bearings mounted on a support about the geometric center of this inner bearing. The outer surface of one of the elementary elastomeric bearings is mounted so as to be locked in rotation in the tubular portion, while the outer surface of the second elementary bearing is fixed to the spindle by means of a thrust device. This thrust device allows the forces due to the centrifugal force to be transmitted to the hub via the inner bearing. According to this invention, the outer bearing comprises an annular elastomeric component which has an inner surface fixed to the spindle and an outer surface which is fixed to the inside of a coaxial sleeve. The above mentioned elastic assembly working in shear is thus housed between this coaxial sleeve and the corresponding inner surface of the tubular portion. The elastic assembly working in shear comprises a shearing annular elastic component of which one surface is fixed to a collar formed by an extension of the coaxial sleeve and which extends perpendicularly to the axis of the tubular portion, and whose other opposing surface is fixed to a collar provided inside the tubular portion. The shearing elastic component is made from a visco-elastic synthetic material whose suitable hysteretic properties give it an automatic damping effect when it is subjected to shearing movements.
French Patent No. 2 358 316 therefore relates to an elastomeric bearing which allows radial deflection so as to provide the articulation assembly with a certain degree of drag flexibility in the plane of the rotor, by rotating about the center of the inner bearing, which then acts as a trunnion. Moreover, to introduce damping into this drag pseudo-articulation, this invention uses elastic elements made of a visco-elastic material exhibiting strong hysteretic properties. This results in a bearing comprising two parts: a first part, made up of the inner bearing and the outer bearing, allowing limited angular deflection about the axes of these bearings, and a second part formed by an elastic assembly working in shear, which allows the tubular portion to move angularly in relation to the spindle with elastic return and damping of these movements.
The type of rotor defined in this patent has the drawback that the connecting structures used between the hub body and each blade are complex structures combining several functions: angular deflection about the blade axis to allow pitch change control, and drag angular deflections with their damping.